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Keeping Transgenic Pollen in Its Place

How far can bees carry pollen? At
least two-thirds of a mile, according to ARS plant geneticist Daniel Z. Skinner in
Pullman, Washington. Why is that important? Because pollen acts as a vehicle to
transport genetic material throughout a plant population or into a related
species.

"In 2004, we can expect to see the first transgenic alfalfa variety on the
market, and others are expected in following years," says Skinner.
"We need this kind of information so that problems don't arise from the
accidental dispersion of transgenic alfalfa pollen to wild populations of
alfalfa."

Skinner and Kansas State University alfalfa breeder Paul St. Amand conducted a
3-year biorisk assessment study. This type of information has never been
obtained for alfalfa. The study was conducted in Manhattan, Kansas, and in
Prosser, Washington, near the ARS Irrigated Agriculture Research and Extension
Center.

Alfalfa, Medicago sativa, has no other close weedy relatives. It relies
on honey bees and leafcutter bees for pollination. The amount of potential
pollen flow between adjacent alfalfa seed-production fields is a key factor in
setting isolation requirements.

In production fields, Skinner and St. Amand planted alfalfa that carried a rare
but naturally occurring molecular marker, which allowed the pollen to be
tracked as if it contained a new gene. They tracked pollen movement from the
marker-bearing alfalfa plants to trap plots planted up to 3,280 feet (1,000
meters) away. Also, they found volunteer alfalfa plants along roadsides and
measured the distance between them and the production fields with an optical
rangefinder or an automobile odometer. Seeds from volunteer plants and the trap
plots were collected and were sprouted, and the sprouts were tested for the
molecular marker. If the marker was found, that seed must have originated from
pollen carried by bees from the production fields.

Leafcutter bees, used in commercial seed production, flew from their hives for
a distance of two-thirds of a mile and back home. According to St. Amand, the
bees would likely have moved pollen even greater distances, but the test ended
at 3,280 feet. He and Skinner used statistical models to estimate that a
minimum isolation distance of 5,109 feet from the hive to any other alfalfa
field may be required to prevent gene flow.

The researchers recommend that producers consider changing their
seed-production practices. They suggest placing bee colonies in the center of
the alfalfa field instead of along the side and surrounding the field with
flowering crops like birdsfoot trefoil or sainfoin so that bees would become
covered with other pollen and no longer transmit alfalfa pollen if they leave
the field. These practices are expected to limit pollen dispersal, but Skinner
cautions that more testing will have to be done.

The ARS study was conducted independently, with partial support from the
Cooperative State Research, Education, and Extension Service and ARS' Biotech
Risk Assessment Program. It preceded a study done by Forage Genetics
International, Madison, Wisconsin, and the North American Alfalfa Improvement
Conference.By Linda McGraw,
Agricultural Research Service Information Staff.